(a) Field of the invention
The present invention relates to a double-filament incandescent lamp bulb assembly, and more particularly to a structure of connecting the lead wires, connected to the filaments, to their respective supports.
(b) Description of the prior art
In case of incandescent lamp bulb assemblies for use as automotive headlights or the like, if provided with two filaments (which will be referred to as "double-filament" type), three or four conductors or wires are led out from the lamp bulb body for connection with an external power source. In the case where three lead wires are provided, the common ends of the two filaments are connected to each other inside the pinched sealing neck of the bulb and further to one of the lead wires for connection to the earth. These lead wires project from the pinched sealing neck as arranged in line in the longitudinal direction of the pinched sealing neck of the bulb. FIG. 1 shows a conventional double-filament type incandescent lamp bulb assembly with an arrangement of four lead wires 2a, 2b, 2c and 2d in line. For the simplicity of illutration and explanation, the two filaments are not shown in the Figure; in practice, however, the lead wires 2a and 2d are connected to the main filament, while the other lead wires 2b and 2c are connected to the sub-filament. These lead wires are fixed with respect to the terminals 3a, 3b and 3c (shown each with a small circle for simplicity of illustration) provided on a holder or reflector 3. The lead wires 2a and 2b are provided corresponding to a common negative-polarity terminal 3a, lead wire 2c is to a positive-polarity terminal 3c for the sub-filament, and the lead wire 2d is provided corresponding to a terminal 3d for the main filament, respectively.
For electric continuity by the above connections, the lead wires 2a and 2b are welded to a support 4a, the lead wire 2c to a support 4c, and the lead wire 2d to a support 4d, respectively, as shown in FIG. 2. Further, these supports 4a, 4c and 4d are installed to their respective terminals 3a, 3b and 3d of the holder or reflector 3 for electric continuity, while the bulb 1 is supported to the holder or reflector 3. The reference numeral 5 shows a plate in which the pinched sealing neck 1a of the bulb 1 is fitted, and the plate 5 is fixed to the holder 3.
FIG. 3 is an exploded perspective view of the above-mentioned conventional incandescent lamp bulb. In this Figure, the lead wires 2a to 2d are cut to appropriate lengths, respectively, and the plate 5 is fitted on the pinched sealing neck 1a of the bulb 1, the lead wires 2a and 2b have their ends spot-welded to the upper portion of the support 4a, the lead wire 2c has the end to that of the support 4c, and the lead wire 2d has the end to that of the support 4d, respectively.
The above-mentioned three supports 4a, 4c and 4d are each formed like an L-shaped lever.
For definite contrast with the embodiment according to the present invention, which will be described later, three orthogonal axes are assumed here as shown in FIG. 3. The Z-axis is directed parallel with the lead wires 2a to 2d, X-axis is in line with the lead wires 2a to 2d, and the Y-axis is directed perpendicularly to both the X- and Z-axes.
The supports 4a and 4d, among the three L-shaped supports 4a, 4c and 4d, which are welded to the lead wires at both extremities, consist of an X-axial connecting arm section and a Z-axial rising section, respectively. The connecting arm sections are opposed to each other and spot-welded to their associated lead wires.
FIG. 4 is a bottom view of the structure in FIG. 2. The connecting arm section (X-axial) of the support 4a is abutted on the lead wires 2a and 2b. The connecting arm section is spot-welded to the lead wires 2a and 2b with them forced in the directions of arrow a and a' along the Y-axis.
The connecting arm section (X-axial) of the support 4d is abutted to the lead wire 2d, and spot-welded to the latter with them forced in the directions of arrows d and d' along the Y-axis.
However, the support 4c to be welded to the central lead wire 2c has the connecting arm section directed nearly along the Y-axis. Therefore, this support 4c must be spot-welded to the lead wire 2c with force in the directions of arrows c and c' generally parallel with the X-axis.
As apparent from the illustration given in FIG. 4, if the lead wire 2c and support 4c are to be spot-welded to each other as forced in the directions of arrows c and c', the spot-welding encounters a difficulty because there is only a narrow space between the area to be welded and adjacent lead wires. In addition, the lead wire 2c and support 4c must be forced to each other in the Y- and X-axial directions, which will complicate the working procedure. Namely, the automatization of the above working procedure, if tried, will necessitate a large, complicate automatic welding machine which requires a large equipment cost and running cost.